Mitosis

Question 0

What are kinetichores?

Answer 0

Chromosome attachment sites where tubulin bind to make spindle poles.

Question 1

What are the key features of cell division?

Answer 1

1. Chromosome condensation
2. Mitotic spindle assembly
   (Correct chromosome attachments)
3. Contractile ring assembly for cytokinesis

Question 2

What are the steps for chromosome condensation?

Answer 2

DNA is formed into chromatin with packed nucleosomes, condensed into chromosome driven by condensin complex. Net result is that each DNA molecule is packed into a 10,000 fold shorter chromosome

Question 3

Describe structure of sister chromatids and when they become tethered together.

Answer 3

Connected at centromere, which connects to the kinetichore, which attaches to the microtubules. Cohesion links chromatids together during DNA replication.

Question 4

Describe mitosis with respect to microtubule dynamics and where microtubule catastrophe happens.

Answer 4

Interphase (centrosome replication), prophase (mitotic aster separation),
Prometaphase (nuclear envelope broken down, chromosomes captured by spindles) CATASTROPHE occurs at highest frequency at prometaphase
Anaphase ( APC is activated and cohesin is degraded)
Telophase (nuclear envelope reformation)
Cytokinesis

Question 5

What types of microtubule play a role in organization in the mitotic spindle?

Answer 5

Mtoc= centrosome center where asters come from
Three types of MT:
1. Astral MT (not connected to anything)
2. Kinetichore MT (from centrosome to kinetichore of chromosome)
3. Polar MT (in relation to chromosomes but not attached to them.

Question 6

What are the potential pathways of spindle assembly?

Answer 6

1. Search and capture (MTs grow and shrink and randomly attach to kinetichore, which stabilizes the MT)
2. Self organization ( MTs grow around chromosomes and motors organize them

Question 7

How are spindles organized? Describe both components and their individual mechanisms.

Answer 7

Motor proteins:
Kinesins are both + and - directed (kinesin 5 cross links and sorts MTs and are tetrameric and + end directed)
Kinesin-14: focus spindle poles
Dynein: - end directed

Question 8

How were metaphase MT dynamics discovered? What was the result?

Answer 8

Express GFP in tubulin and photobleach. Bleached zones move poleward which means polymerization happens at kinetichore. Depolymerization happens at minus ends. But during metaphase total length of MT doesn’t change

Question 9

How does the spindle assembly checkpoint occur?

Answer 9

To initiate anaphase, all sister kinetichores just be attached to opposite spindle poles. After this requirement, the inactive APC (anaphase promoting complex) is activated by cdc20. APC then ubiquitylates securin which is attached to separase. Degradation of securin activates separase which cleaves cohesin. Then the sister chromatids separate and anaphase begins.

Question 10

For anaphase to happen, spindles must pull the chromosomes inward toward the centrosomes. How does this occur?

Answer 10

Determined by photobleaching at anaphase, MT depolymerization occurs at kinetichore (pacman) and at centrosome.